Automatic telephone system



F. LUBBERGl-:R I

AUTOMATIC TELEPHONE SYSTEM June 14, 1927,

June 14, 1927.

F. LUBBERGER AUTOMATIC TELEPHONE SYSTEM Imranlm" Il' Lubbsr er F. LuBBERG-ER UTOMATIC TELEPHONE SYSTEM 3 Shees-Shaet 3 Fil'ed July 2. 1925 N S I.

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Fmi L ubber' gf' l 45ml@ Patentedvilune 1 4, 1927.' h

UNITED sf'ra'lrsn PATENT. OFFICE;

yFRICTZ LUBEBGEIB, 0l' BEBLIILSCMABGENDOBF, GERMANY, ASSIGNO T0 SEHEN S y BALSXE AKTIENGESELLSCHAFT, 0F WEBNEBWEBX, IBEBLIZBI,v GERMANY.

YAu'rolu'rrc TELEPHONE sYs'rxi.

applicaties alea my a, was, semina. 41,035 and m @my my 1a, im.

The invention relates to automatic telephone systems comprising main and subex' changes. 'lhe latterA onl contain a fraction of the switches requlred for setting up a connection. -Their function is to colleentrate the trailic over a number of 1i htly loaded subscribers lines and to forward traffic over a few trunk lines, which are thus more heavily loaded. These subexchanges can'for example beinstalled in every block of mansion flats in a town and serve the trathc to the subscribers thereat. The method of operating lthese lines should be the same as that for main exchange subscribers,

because thesubscribers of a town cannot be required to observe two different ways of setting up calls for abusiness address andfor a private address. Hence the subscribers station must therefore be provided .with the standard instrumentl without keys or the like. All the operations called for by the' tariff, such as single metering, repeated metering andtime metering, of suburban calls, and releasing a' local connection for the benefit of toll calls5` must. be the same for sub-exchange subscribers asfor other subscribers lines, because all the'traic must b e able to pass over the switches at the main..

exchange. v

The amount of'ruanual attention required by the sub-exchange should be Vreduced to switching i calls).

take place at the endof the conversation,

a minimum. Y- HenceY itis desirable that' all o perations should be effected. by means of re ays and no batteries of accumulators should be installed. Arrangements are known whereby battery f cedcurrent for subscribers lines Ysuch as extension stations is passed over one leadv forcallstb the town -area',an'd whereby battery current constantly passes over the other lead for feeding -the calls set up between subscribers of the same sub-exchange. v

Y The main object of the invention isto enable the different operations to be vperformed, -which mostly are combined with the release (for exanple metering and toll The time zone metering can Lonly because the duration of the call aiects the amount to be metered, andlocal calls may have to be released cmpulsorily and prematurely furthe benefit of toll Hence The parts numbered 200 belong to a number a0 I ofthe subimpulse receiving switch, which is used vfor selecting a sub-exchange subscribers line. The switch is associated with the trunk line to-a subscribers line. Several trunklines can behprovided. F ig.` 1 in severalplaces indicates a second trunk lineVL 1I,- which will be more particularly referred to hereafter. In place ofthe single subscribers line 300, any number of subscribers lines can' Abe installed Without altering theV circuits.

The condenser'COU supports the energiza'- vVL I. All the parts numbered 300 belong tion of the rela-ys of the sub-exchange, which likewise. obtain their energizing current over the chokingdevicesDR and R 400.

The Fig. 2 shows thev arrangement of the' main exchange. VW 500 is a preselector at the end of the trunk line VL I. Alt-ftheparts numberedrOO belong to this'preselector. All the parts numbered 400 belong to fa relay set; which associated withthe trunk linev VL I.

A preselector VWH indicates a subscribers connection tov the main exchange. 'GW 600 is a first group selector,j which for example is assumed to beY a switch having lifting and rotary. motion. A secondpreselector canbe inserted between the preselector and this group selector,`but for the sake of simplicity, such a second preselector has been omitted. f

GW 700 is afurther group selector. It can `forni-a second or third group selector or the like. The type of this switch is of little importance.

The Fig. 2' only shows those circuits of a known system that are required for describing the present "invention,

(See vfor example the description' of the Siemens &

-Halske Asyst-em in Lubbergers book entitled Fernsprechanlagen .mit Whlerbetried second edition.) Y

The subcmbeai-N 30.0 (Fig. 1) seta up a call 1 to a ysabu/rb.

On taking'dwn his receiver, the following circuit is closed:

1. Earth, Acalling relay A- 300, back contact t 304,'number dial contact nu 300, Subscribers instrument N 300, back contacts -t 302-and asp 202, choke coil Dr 100, lead bd 1030i the trunk line VL I (Fig. 2), relay erate.

R 400, back contacts 'v 401 and cf 401, battery, earth. 4The relays A300 and R 400 op- The coupling relay K 100 at'its' front contacts -c 101 and 102 connects the lspeaking. leads ad 102, bd 102 of the calling line N 300. to the-leads ad 101 and bd 101 of the trunk line VL I. A condenser CO 101 pre* 'vents direct current passing from the lead bd 101 to the leadbd 103. The vfront contack k 103 closes the following circuit:

2.' Earth, cut-0H relay T 300, lead dd 102, front contact 7c 103, coupling relay K 100 winding II, lead dd 101, relay C 100 winding II, battery lead batt 101.'

The front contacts k 104 and c 105 prepare the meter circuit'by connecting it to the trunk line VL I. -The cut-oit relay T 300 opens ,the calling circuit at the back contacts t 302 andt 304; at the front contacts t 301`and 15303 it connects the trunk line VL I to the subscribers line; and at the front contact t 305 it short circuits the' calling relay A 300. The relays T 300, K 100 and C 100 remaincnergized until the release of the connection- At the main exchange (Fig.l2) the calling relay R 500 of the ypreselectorVW 500 isl connected to battery over the front contact r 401 of the relay R 400. When the lcalling station N 300 is switchedv through to the trunk line VL I, the calling circuit for the preselector-(Fig. 2) is closed over:

3. Earth, battery, front contact r 401, calling relay R 500, back contact t 501, lead ad 103 (Fig. 1) back contact l 103, lead ad 101, ,front Contact c 101, lead ad 102, front contact t 301, subscriber' N 300 number dial contact' 300, 'front contact t 303, lead bd 102, vfront contact lc 102, lead bd 101, relay release its armature.

the trunk line VL II into use, thus ren-- dering the second trunk line accessible.

At the main exchange (Fig. 2) the preselector VW 500 is started up:

5. Earth, battery, front contact r 502, back contact t 504,`rotaryma et D 500, interrupter, earth. The prese ector rotates until -an idle group selector is found, whereupon `the following test circuit is closed:

6. Earth, battery, front contact r 501, cutoil' .relay T 500windings II and I, wiper @we of the preselector, lead ed 601, relay C 600 winding I, off normal contact k 601, earth. The relaysT 500 and C 600 operate. The back contact t 501 disconnects the calling relay R 500, while the front contacts t 502 and 503 switch the trunk line VL I through to the group selector GW 600; the back contact t 504 interrupts themotor circuit of the preselector, while the front contact t 505, by "short circuiting the winding II of the cut-off relay T500, marks the line engaged in known manner. After the calling relay R 500 has been released, the marking engaged circuit is maintained over the segment Sg 500 and the Wiper lvwd of thev preselector.

After the calling relay R 500 has been disconnected, the lead ad 103 is switched through over the preselector wiper /vwa and the lead ad 601 to the `line relay A 600 of the group selector, and relay A 600 is operated in the same circuit as the relay R 500 was previously operated. The following circuit is closed over the wiper luwb of the preselector:

p 7. Earth, battery, back contacts cf 401 and 'v 401, relay M 400, front contact t 503, preselector wiper lvwb, lead 'bd 601, winding I of the relay B 600, earth. The" relays B 600 and M 400 operate. The latter energizes the slow releasing relay V 400 over:

8. Earth, frontcontact my 403, relay V 400, battery, earth. The calling subscriber now hears the exchange calling signal over:

9. Earth, relay B 600, winding II, offnormal contact la 602, condenser CS 600,

buzzer tone.

Thereupon the subscriber N 300 transmits the number impulses and his number dial at nu 300 opens and closes the loop in known manner. These interruptions cause the line relay A 600 of the group selector GW 600 to to retain its armature attracted during the The relay B 100 is j M ultz'ple metering.

When the callingl subscriber hangs up his receiver, the relays B 100 and A 600 are deenergized. The former closes the following circuit:

11. Earth, back contact b 102, front contact d 102, relay U 100, battery lead batt 101. The back contact u 102 disconnects the condenser COU in order that this large condenser shall not delay the deenergization of the holding relays by its .long maintained discharge during the 4subsequent release. The front contact u 101 closes the metering circuit in the manner now to be described.

When the line relay A 600 at the group selector is deenergized, its contact a 602 short circuits the relay C 600, which releases its armature after a little while. The known roup selectors.

descriptions of the system mention that the lead bd 701 outgoing from the group selector is connected to battery for the purpose of preparing the metering operation. (One method of ell'ecting this operation will be described hereafter' for a call toithe subscriber N 300.) At the group `selector the relay Z 600 is energized over: n

.12. Earth, battery on the lead bd 701, switch wiper gw 602, front contact p 602, back contacts u 601 and c 601, rela Z 600, oinormal contact k 603, earth. T e relay 4Z 600 closes the following meter circuit:l

13. Multiple ymetering device MZ, winding II of the relay V 600, front contact z 601, lead cd 601, preselector wiper v fwc, cut-off relay T500 wind-ing I, and parallel thereto meter relay ZR 500, back contact cf 402, front contact t 505, segment Sg 500, preselector wiper fv'wd, battery, earth. Multiple metering, devices are known` They comprise for example interrupting discs, which transmit one or more earthed current impulses accordin to the positioning of the t will be assumed that for t e connection set up it is necessary to operate the meter three times. Hence the multiple metering device transmits three current impulses from earth. Each current impulse nearly short circuits the resistance W 601, thereby considerabl increasing the current in the lead cd 601 t ree times 1n succesthe main exchange `the relay sion, so that the relay ZR 500 is energized three times. These metering impulses maintain the relay V 600 energized over its winding II while they are being transmitted. At each of the three energizations of the relay ZR 500, the latter. closes the meter circuit for the subscriber over: i

' 14. Earth, frontcontacts a1' 502 and -t 502, lead ad 103 (Fig. 1) back contact l 103, lead ad 101, front contact u 101, back contact zfv 101, front contact k 104, lead zd 102, me-

ter Z 300, lead zd .103, front cont-act 16105, l

battery lead batt 101.

At the end of the metering impulses, the connection is released. The relay V 600 releases and closes the release circuit for the group selector over: 15. Earth, battery, release magnet-M 600,- back contact /v 601, off-normal contact lc 603, earth. At its back contact m 601, the release magnet M 600 opens the locking circuit'over the lead cd 601, thus causing the release of lthe cutof relay T 500 at the preselector VW 500. The front contact t 503 opens the holding circuit for the relay M 400, which in turn opens the energizing circuit for the rela V 400. 'The latter being very slow acting, attery is disconnected for a while 'from the lead bd 103 over the .front contact m'401 and the back contact 'v 401. Hence at the sub-exchange the lead batt 101 is dead, and

since the condenser COU is also disconnected at the back contact u 102, all lthe relays hitherto maintained energized are released, namely the relays C 100,1( 100, T 300, D 100 and nally the slow actin relay U. 100. Thus all the relays at the su-exchange have been returned to their normal osition. At

400 is deenergized. 'During the short interval between the release of the relay T 500 and the release of the relay R 400, the calling relay R 500 is connected to the lead ad 103 over the front contact-r 401 and the back contact z.

.501; but the contact u 103 at the sub-exselector VW 500 to'return to' its normal position.

17. Earth, interrupter, motor magnet D 500, back contact t 504, segment Sg 500, preselector wiper vwd, battery, earth. This circuit remains closed until the wiper lpwd leaves the segment Sg l500.

Rekase "wz'tlwut metering.

Should the wanted subscriber fail to an'- swer the call or be engaged, there will be no metering potential (battery) on the lead bd 7 01 outgoing from the group selector. Hence the metering relay Z '.600 does not operate and no metering impulses are transmitted. A little while after the Contact c 604 has been opened, the slow acting relay V 600 will release its armature and will bring about the release without the meter havin been operated.

@azz zo me .gutem-bef N 00.

lll

ing l of relay C 600, lead ed 601, preselector wiper multe, relay TH windings I and II, battery, earth. The subscriber positions the group selector GW G00 onto Athe seventh'- level and the connection is extended in known manner to the group selector GW T010. When it has thus been switched *througln the test relay l 600 at the group selector GIV' 000 is operated over:

19. Earth, windings II and I of relay P .'-11 000, front contact o 602, wiper gw 603, lead l 701, relay C 700, battery, earth. Thereby the relay C V700 is also operated.

' 'lhe subscriber NH 'then positions the group selector GIV 700 onto thel fourth level and the` connection is switched through to thev trunk line ad 401,' bd 40,1, ed 401', hence the test relay P 700 is operated over:

20. Earth, relay 13,700, front contact e 701, wiper gw 703,'lead ed 401, back Contact 4f. -r 402, preselector wiper- @we (in its normal position), windings I and II of relav' T 500,-

preselector wiper vwd, battery, earth. The relay T 500 having likewise been operated, the relay-M400 is operated oyer:

' 21.' Earth, battery, .back contacts cf 401 and 'v 401, relay M 400, front Contact t 503, preselector wiper fvwb, choking coil Dr 402-, earth. The relay M 400'energizes the relay V 4'00 over:

,400, battery, earth'.

In the lead ed 401, the contact m' 402 is closed before contact 'v 402 is opened. The

contact t 502 closes the following circuit:

23. Earth, battery, relay C 400, back contact 'a 401, preselector wiper fvwa, back con- .'tact er 501,V front Contact t 502, lead 'ad 103 (Fig. 1), back ontact Z 103, .lead ad 101,

back contacts. u 103, e 101 and oir 101, callo ing relay AR* '100, earth'. TherelaysC 400 and AR.100 `are operated. l

At the .repeater a relay Q 400 is operated as follows:

24. Earth, battery, relay Q, 400, f rontconwinding I also closes a holding circuit 101 22. Earth, front contact m 403, relayV.

tacts c 401 and m 404, earth. Relay Q 400 locks itself over contact Q 401.l Relay AR 100 connects up the switch NE 200, and the energization of the relay lVB 200 is caused in the following circuit:

25. Earth, relay WB 200, front contact ar 103, back contact c 102, battery lead batt 101, choking coil Dr 100, lead al '103, (Fig. 2) .relay R 400, front cont-act m 401, back contact lef 401, battery, earth. The relay R 400 also operates without having any urther elect. The relay WB 200 closes the contact/wb 201.

The calling subscriber NH transmits three current impulses whereby the relay A 600 at the group selector GIV G00 is oscillated three times and it closes three times'the following circuit:

26. Earth, back contact a 601 front oo ntacts e 603, p 601, group selector wiper gw 601,1eadad 701, front contact p 701, vgroup Selector Wiper gw 701,.lead ad 401, relay A 400, battery, earth. The relay A 400 opens three times the above described circuit over the lead ad 103. The relay C 400is not to release during the short current interruptions, this being achieved by a mechanical retarding device.

The relay AR 100 (Fz'g. 1) 'oseilldtes three' tz'mesf-Fz'rst current impulse.

27. Battery lead batt 101, back contacts c 102 and ar 102, front contact 'wb 201, relay J C 200 (this does not release its armature durin the impulses, because it is slow act ing), ack contact diff 202, Winding I of relay J 1, back contact p 201, earth, and paral- I lel'theretoover T 200 Winding I, earth. The relay'sJ 1 and T 200 are operated. Relay T 200 closes the following holding circuit for itself:

28. Earth, winding II of relay T 200,l front contact t 204, back contact t 802, front contact 'wb 202, battery,earth. Relay J 1- itself: o

29. Earth, front contact' fi 11','winding II of relay J -1, front contact t 203, relay P 200, backl contact e 102, battery lead batt 101. The relay B 200'operatesand opens itscontact p 201. The front contact t 201 connects both windings of the differential relay Diff' to earth, and it does not operate so lo'ngas the contact ar 102 is closed.

Emi of the ,im impulse.

The;back contact var102 is-opened, hence relay Di# operates over: Y I

30. Earth, doublefront contact' t 201, WindingII of the relay Dif, back contact e 102, battery lead batt 101. 'Ihe back contact' dif 201-disconnects winding I ofthe relay D117?E from theimpulse lead, while the front' Asp contact dfi/f 203 prepares the energizing circuit for the second switch relay J 2.

102 and a1- 102, front contact 'wb 201, relay J C 200, front contact di# 203, winding I of relay J 2, double front contact z' 11, earth,

and parallel thereto relay T 800, earth. The relay J 2 winding I and relay T 800 operate. The diferential relay Di# remains energized over the front contact t 801. The contact t 802 opens the holding circuit of winding II of relay T200, which is deenergized and falls back. The relay P 200 remains energized in the holding circuit of relay J 2 as follows:

32. Earth, double front contact c' 21,wind ingy II of relay J 2, back contact t 202, relay P 200, back contact c 102, battery lead batt 101. The relay J 1 is'deenergized because'l its holding circuit over the windingII is opened at the contact t 203.

E mZof the second impulse.

ing circuit of relay Dz, which thereupon releases.

Third impulse.

The relay AR 100 again releases and closes the following circuit:

33. Battery leid batt 101, back contacts c 102 and 'a1' 102, front contact fw?) 201, relay JC 200, back contact diff 202, third switch relay J 3 winding I, double front contact i 21, earth, and parallel thereto relay T 200 winding I, earth. The relays J 3 and T 200 operate. The front contact t 201 prepares the circuit for ener izing the relay Da", and at contact t 203 it c oses the following holding circuit for relay J 3:

34. Earth, double front contact i 31, wlnding II of relay J 3, front contact t 203, back contact c 102, battery lead batt 101. The front contact t 204 closes the holding circuit for relay T 200 over its winding II.

l. ized, because the numerical selection hasl l'geen completed. Hence relay JC 200 after' a little while releasesjits armature. 4 Its back contact c 201 closes the following circuit:

35. Earth, relay Asp 200, back contact 'ic 201., front contact p 202, relay M 200, fbattery lead batt 101. The relays M 200 and 200 operate. asp 201 opens the takin into use circuit, so

that during the succee ing testing time no subscriber of the sub-exchange can take a The latter at its contacty M 200 andv trunk vline into use. The second back contact asp 202 opens the energizing circuit of the calling relay A 300, etc., so that only the calling relay of the wanted subscriber N300 can be operated. The front contact 'ra 202 closes the following exciting or test clrcuit:

36. Battery lead batt 101, front contact fm. 202, relay F 200 (which is not senstive), front contact fi 32, relay A 300, earth. Relay A 300operates, while relay F 200 does not attract its armature. The relayA 300 closes all its contacts a 301, etc. (a 302 in a corre'- sponding position in the trunk line VL II, 1s not shown). The relay M 200 has enabled the trunk line to be taken into use over the Contact m 201 after it was marked engaged by contact asp 201. Front contact a 301 -closes the following coupling circuit:

37. Earth, front contact a 301, winding I of relay K 100, lead ed 101, winding I of relay C 100, front contact lml 201, ringing relayl L 100, battery lead batt 101. The relays K 100 and L 100 operate. The former (K 100)m couples the wanted lineN 300 to the trunk line VL I in the manner above described, and also closes the holding circuit 38. Earth, relay T 300, lead dd 102, front contact c 103-relay K 100 winding II, lead dd 101, winding II of relay C 100, battery lead batt 101. The relay T 300 switches the line through at the contacts t 301 and t 303, and .at t 305` itshort circuits the relay A. This short circuit so increases the' current in the relay F 200 that it operates without having any action at the present time.

The ringing relay L at the back contact Z 101 disconnects the busy tone relay BR 100 before the energizing circuit is closed at contact f 201. Contact Z 102 closes holding circuit for the relay L 100 as folows:

39. Battery lead batt 101, ringing relay L 1.00, front contact Z 102, back contact b 102, earth. The front contact Z 104 switches over the leaded 101 to the source of ringing current :v

40. Source of ringing current, front contact Z 104, lead ad 101, front contact k 101, lead ad 102, front contact t 301, subscribers lll instrument N 300, number dial Contact 'v nu 300, front contact t 303, lead bd 102, front contact k 102, lead bcZ 101, relay B 100.

earth. The relay B 100 is notoperated alternating current. A

The relay C 100 at contact c 102 opens the holding circuit for all the relays of the switch NE 2 00,v hence the relay P 200 opens the contact '202, thereby causing the relays p 200 to release. Thisl restores (at asp 201) the possibility for the other trunk lines VL II etc. to be taken into use. The contact 'c 101 disconnects the calling relay AR 100 and opens the lead ad 101. At the main exchange, the relay C 400 re'- leases its armature and the relay. F 400 is operated over:

41. Earth, battery, relay F 400, back contact e 402, front contacts q 402 and m 404, earth. The relay locks itself over contact f 401. When the subscriberN 300 answers the main exchange the relay C 400 is now operated for the second time, and the metering relay Z 400Sisenergized as follows:

43. Earth, battery, 'relay Z 400, back contact ef 403, front contacts f 402, c 403, g 402 and fm 404, earth. The relay Z 400 locks itself over the contact e 402, and at contact` e 401 it applies the metering potential battery to` the leads bd 401 and bd 701. The subscribers speak to one another.

Subscriber N 300 `s engaged.- I

Then the snbscribers li'ne N 300 is .taken intouse lfor incomingv or outgoing calls', the relay T 300 is energized, and in every case the relay A 300 is short circuited over contact t 305. When the exciting circuit is closed over contact m 202, relay F 200 and the front Contact z' 32, enough current passes to immediately energize the relay F 200.K y The ringing relay L 100 is not energized because relay A 300 is not energized, and therefore does not close the energizing circuit for relay L 100. .Hence the busy tone relay BR 100 is energized as follows:

44. Battery lead batt 101, winding I ofA relay BR I100, front contact f 201. back contact Z 101 earth. rIyhe relay BR 100 disconnects the calling relay AR 100 at the contact br 101 and locks itself in the following holdl ing circuit:

45. Earth, winding Hof relay D 100, winding II of relay BR 100, front contact vbr 10'2, back contacts e 101 and u 103, lead ad l101, contact Z 103,1lead adV 103, (Fig. 2)

l front' contact t 502, back contact er 501, preselector wiper lvfwa, back contacta 401, relay C 400, battery', earth. The ,winding III of the relay BR 100 carries the 4busytone bs, which is repeated-f to the winding II.- This busy. tone reaches the calling subscriber NH over the lead ad 103. The relay D 100 operates and prepares the release; the relay C 400 remains energized; While relay 'F 400 and later on Z 400 are not energized, hence meteringdoes not take place.

Metering and release at the end of conmersd.

The relay Z 400 at its contact z 401 has connected'the metering potential battery to the leads bd 401 and bd 701. When the calling subscriber NH hangs up his receiver, the relay A 600 falls back and brings about the metering operation in the manner'before described.. -The'metering operation having been completed, the relay Vl 600 releases and, by opening contact c 602, it opens the holding circuit for the relay C 700. This also releases and at contact e 701, it opens'the holding circuit of the relay T 500, which resumesA its norma-l position. At Contact t 503 the holding circuit for the relay M 400 is opened, which at contact m 401 disconnects battery from the lead bd 103. All the relays at the sub-exchange, which have been maintained energized overthe battery lead batt 101, are released.

Release after a Zbnehas been found engaged.

At the sub-exchange, holding circuits have been established over the lead batt 101. The windings II of the relays BR 100 and D 100 have been connected to the lead ad 103. In the main exchange the holding battery is disconnected from the lead bd 103, at the contacts m 401 and e401, and from the lead I ad 103 at the contacts t 502 and r 401; vthereby causing the release of the relays still locked at the sub-exchange. y

Suppressing the .metering and-efeetz'ng the release, when the wanted subscriber N 300 does not answer.

The second energizaton ofthe relay C 400 does not occur, at the repeater, because this energization by. the feeding current would take place ywhen the wanted subscriber answers the call.. Hence the contact e 403 remains open and the relay Z 400 is not energized. The release is effected. as before gdescribed by the deenergization of the relay Suppresizng the metering .of incoming vIncoming calls to the subscriber N .300

'must not operate the meter Z 300. Hence,

when the relay AR 100 operates, it energizes as follows a relay ZV 100, which prevents metering taking place:

46. Earth, front contact ar 101, relay ZV 100, battery lead batt 101. The relay ZV 100,1ocks itself over its front contact zv 102.

.The back contact z/v 101 vopens the circuitv for energizing the meter Z 300. The relay ZV 100. is also used for twitching over to thding relays A 300 etc. over:

trunk line VL II the taking into use circuit,

which is disconnected from the line VL I AZZ trunk Zi/nes VL are engaged.

When the taking 1 into use circuit is switched over from the last trunk line (for example VL II), this being elected for example by the relay D 200, which corresponds to the relay I) 100, the relay GB is then energized as follows:

47: Battery lead batt 101, back contact asp 201, contact zo 103 (or zfv 104), front contacts d 104 and, (l II, relay GB, earth. This relay connects a busy tone to the call- 48. Earth, busy tone windino bs I, front contacts bg and a 310, relay 300, earth.

Thus the calling subscriber is notified that all the trunk lines are engaged.

Local calls, that is to say calls between subscribers belonging to the same sub-exchange, are few in number'when compared with the total traffic of the sub-exchange. To set up such local calls, the calling subscriber4 calls the wanted subscriber' over the trunk line, for example VL I, and over Jthe switches at the main exchange and a second trunk line VL II. y

Toll calls occur seldom for the subscribers lines, to which the present invention relates;

hence a somewhat umsy method of operating is. admissible. The Fig. 2l shows one method of dealing with such calls.

The toll. exchange calls the wanted subscriber in the usual manner. When the subscriber answers', the toll connection is set up over this route. If the operator finds the line engaged, the toll operator sets a toll offering switch on the engaged subscribers line, this being done by setting 4the offering switch, by means of-number impulses, in succession on the trunk lines VL I, VL II, etc.,and asking for thel wanted subscriber N 300. The toll operator then informs thesubscribers that a toll c'all is waiting for N 300. and that the local connection will be released. The subscriber N 300 thereupon hangs up his receiver and releases the connection. Thereby one of the trunk lines has become disengaged; and lthe `toll exchange nw sets up again an ordinary connection. If at this 'moment `the wanted subscriber 'should also be called by another. party, the

toll yoffering procedure would have to be repeated. l

lThe .toll exchange canalso compulsorily release the local connection by energizing the relay CF 4,00 (Fig. 2) from the toll cordcircuit. The""'relay CF 400 opens the contact cf 401 and thusl interrupts the battery con` necting lead for all the relays at the sub-exchange, thereby causing them to release.

The contact cf 402 o ens the incoming test lead, so that the trun line cannotvbe called whilevthe toll exchange is effecting the release.

The Fig. 3 shows a modification of the repeater at themain exchange. In the -arrangement vabove described the subscriber Nv 300 doesnot become free when he hangs up his receiver after receiving an incoming call, because the release is effected from the calling end (NH). The circuit shown in Fig. 3'. enables the subscriber N 300 as well as the trunk line VL to fbecome free as soon as the receiver is hung up after every type of call. For this purpose the repeater (numbers 400 etc.) is located at the last group selector, and after a call has been made tothe grou of stations, to which N 300 belongs, the wlper leads at the group selector yare opened as soon as the receiver is hung up.

In the Fig. 3 the circuit of the preselectgr VW 500 is only indicated, it is quite similar to the circuit shownl in Fig. 2.

It has already been mentioned above that for calls outgolng from the group of stations N 300, the station N 300 as well as the trunk line VL are released (become free) after the receiver has been hung Aup at N 300 and after metering has been effected.

The method of setting up a call to the station N 300 will now be described.

The subscriber NH (Fig. 2) sets the group selector GW 600 onto the ninth level. When it is switched through to the group selector GW 900 (Fig. 3), the test circuit (Fig. 2) is closed as follows:

49. Earth, windings II and I of relay P 600, front contact V 602, group selector wiper gw 603 (Fig. 3)-,lead cd901, .olf-normal contact k 901, relays B 900 winding' I and C 900 winding I, battery, earth. The relays P 600, B 900 and C 900 are operated. The front contact c 901 closes a holding circuit over the relay C 900 winding II independent of the olif-normal contact c 901. At `the contacts b 901 and b 902, the relay B 900 connects the line relays A 900- and B 900 winding II to the incoming speaking leads ad 901 and Zul 901. The calling subscriber transmits four impulses, whichcause the relay A 600 (Fig. 2) to oscillate'four times. At each release, a slow acting relay U 600 is energized as follows:

' 50. Earth, front contact-.c 604, relay U 600, back contact a 602, winding I of relay` V 600, battery, earth. During the transv 1go mission of impulses, the following circuitiis closed by the relay U 600 v51. Earth, battery, resistance (Fig.

front contacts u 602 and p 602, switch wiper gw 602, Fig.,3), lead bd 901, front cont-act b 902, winding II of relay B 900, earth. The relay B 900 remains energized` during the impulse transmission, although the o'- normal contact 901 was opened at the first step.

Each time the oscillating relay A 600 releases its armature a circuit is closed over (Fig. 2) l 52. Earth, back contact a 601, front contacts c v603 and p 601, selector brush gfw 601- (Fig. 3), lead ad 901, front contact b 901, relay A 900, battery, earth. The latter closes the following circuit four times:

53. Earth, front contacts 5.904 and a 901, lifting magnetl I-I 900, battery, earth. The oli-normal contacts la 901 and k 902 are switched over at the first step.

contact le 902, back contact p 901, front con-- tact c 903, back contacts s 404, and a 902, rotary magnet D 900, battery, earth. `Upon attracting its armature, the rotary magnet closes its contact d 901. hence the relay A 900 is operated in the following circuit:

V55. Earth, 'front Contact d 901, relay A 900, battery, earth. contact a 902, opens the motor magnet circuit, hence the rtoary magnet D 900 releases. Thus the relay A 900 and the rotary magnet D 900 function as a self interrupter until the switch test wiper gw 903 finds an idle line and closes the following test circuit:

56. Earth, windings I and II ofprelay P 900, front contact c 901, back contact s 403, switch wiper. gw 903, lead ad 401, preselector` wiper lvwo, cut-off relay 'I 500 windings I and II, battery, earth. The relay P 900 opens the motor magnetcircuit at the'contact p 901 and at the contact p 902 it marks the selected line engaged. The contacts pV 903, p 904, p 905, p 906 connect up the repeating device relay A 400, relay C 400, choking coils Dr 403 and Dr 402. The rest of the setting up Aof the connection to the subscriber N 300 takes lace in the manner previously described. t should be noted that the relay C 400 is energized until the end of the last numerical selection.A Relay (2,400 (Fig. 3) had also operated:

57. Earth, battery, relay (2,400, front contacts c 401 and c 904-, earth. After switch ing through to the Station N 300 has taken lace at the'sub-exchange, the relay C 400 alls back 'for th'e first time'and energizes relay F 400. When the subscriber N 300 answers, the relay C 400 again operates and energizes the meter Z '400 as beforeV de The latter, at its back A l it interrupts the leads to the preselector V W 500. whereat the 4cut-off relay T 500 falls back. The release of the relay T 500 renders the trunk line VL free vas before described. The group selector GW 900 is not yet released. The metering circuit is prepared by the closing of the contact .e 401.

The meteringand'releasing'operations for the group selectors GW 600 and GWV 900 vhave 'been described above.

When the toll operator compulsorily releases a local connection, metering is to be suppressed. If the station N 300 has originated the call, metering can be suppressed by opening the circuit of .the meter relay ZR 500 at a contact of 402of the cut-oit relay CF 400. For the purpose of suppressing the metering, of incoming calls, the metering relay Z 400 can be released by a contact l,What is claimed is:

1. vIn--a telephone system, a main anda sub-exchange, a trunk line between said exchanges, said sub-exchange containing switching equipment comprising only relays, said switching equipment automatically operating to' seize said trunk in response to the initiation of a call from said sub-exchange, and directively operable by impulses received over said trunk on calls from said main exchange to 'select a called line in said sub-exchange.

2. In a telephone system, a main and 'a sub-exchange, lines in each exchange, automatic switches in the sub-exchange com rising only relays, trunk lines between sai exchanges terminating in an automaticswitch in the main exchange and in the switching equipment at the su exchange, said switch-v ing equipment operated to automatically select a trunk to the main exchan when a subscriber in the sub-exchange initiates a call and operated directively over one of said trunks to select a. line in the sub-exchange l said switching equipment and over said trunk, and means for operating and holding said sub-exchange equipment by current received from said main exchange source over said trunk.

4. In a telephone system, a main and a sub-exchange, a trunk line between' said exchanges, said subi-exchange containing switching equipment comprising only relays, a source of current at said main exchange, and means for feeding operating current to said sub-exchange equipment from said main exchange source over said trunk line.

5.- In a telephone system, a main and a sub-exchange, subscribers lines terminating in each, auto-matic switches in the main ex change, relay switching equipment in said sub-exchange, trunk lines between the exchanges terminating in an automatic switch in the main and in said switching equipment in the sub-exchange, means responsive to the initiation of a call by a sub-exchange subscriber for connecting that line to an idlc one`of said trunk 'lines and for operating said main exchange trunk switch to extend the connection to an idle-selecting switch, and means for holding said engaged subexchange equipment in operated position by current fed over said selected trunk line from said main exchange.

6. In a telephone system, a main and a sub-"exchange, subscribers lines terminating in said exchanges, trunk lines between said exchanges, switching devices in said exchanges, means for extending a talking con-l nection from a calling line in said main exchange through switching devices therein over a trunk line to said sub-exchange through switching devices therein to a called line, and circuit means such that during coni versation current flows in the same direction over both sides of said trunk'lin'e, current being supplied to the sub-exchange subscribe-rs transmitter over one lead thereof, and current for holding the sub-exchange switching devices in operated position being supplied over the other side.

7. In a telephone system, a main and a sub-exchange, a two-way trunk line between said exchanges, said trunk line terminating in relay switching equipment in said sub-exy change andin anon-numerical line switch switch in said main exchange, other automatic switches in sa1d main exchange, a home position for said line switch, circuit means.

for rendering said trunk line selectable for calls from said main to said sub-exchange when said line switch-is in its home posiforcausing said-line it m,

. A, e, "lts home position in search an idle one of said automatic switches when the trunk is seized through change,

8.l In a telephone-system, a'main and a sub-exchange, subscribers lines terminatin in each exchange, trunk lines between sai exchanges, switching equipment in said ex changes, means for extending a talking connection between a main and a sub-exchange subscriber by way of one of said trunks and through certain of said switching equipment, and means at Said main exchange for controlling the release of said sub and main exchange equipment involved in the connection.

9. In an automatic telephone system, a

main and a sub-exchange, a trunk between said exchanges, a branch of said trunk terminating in a toll board, automatic switching devices in said exchanges, subscribers lines terminating'in said exchanges, means for operating said switching devices to extend main to sub-exchange calls over said trunk line, battery current for said subexchange switching devices being fed over said trunk line, and means enabling an operator at said toll board to seize said engaged trunk by way of its branch and to release said established connection by interrupting the battery supplyin said trunk. .F 10. In a telephone system, a main and a sub-exchange, switching devices in said exchanges, subscribers lines terminating in said exchanges, a trunk line between said exchanges, means for establishing a talking connection between a main and a sub-ex change subscriber over said trunk line, circuit means such that the battery current for operating said sub-exchange switching devices is supplied from the main exchange over said trunk, said circuit means being so arranged that the hanging up lof the receiver of the sub-exchange telephone re- 'leasesa relay in the main exchange by opening one side of said trunkand that the subexchange switching devices are released by the subsequent opening of said trunk line by means controlled 4by the deenergization of said relay.

11. In a telephone system, a main and a sub-exchange, subscribers lines terminating in said exchanges, a trunk line between said exchanges, automatic switches in said .main exchange, relay switching equipment in sai-d sub-exchange, means responsive to a certain number of digits sent from a calling one of said main exchange subscribers? lines for extending that line through certain of said automatic switches into connection with a called one of said main exchange subscribers lines, and means responsive to the same number of digits sent from said calling line for extending 0f that line through certai Said automatic switches, over said trunk line through said relay switching equipment, and

vinto connection with a. called one of said the Y switching equipment of the sub-exsub-exchange .subscriber-s lines.

12.` In a. telephone system, a. main and a' ILO sub-exchange, subscribers lines terminating 1n each exchange, trunk llnes between said exchanges, switching equipment 1n said exchanges, means for extending a. talking conneetion between afmain and a sub-exchan e subscriber by Way of one of Said tr s and through certain of said switching 

